Apparatus and method for virtualizing a queue pair space to minimize time-wait impacts

ABSTRACT

An apparatus and method for virtualizing a queue pair space to minimize time-wait impacts. The apparatus and method allocate virtual queue pairs from a virtual queue pair pool of a node to connections between the node and other nodes. The connection is established between a physical queue pair of the node and physical queue pairs of other nodes. However, from the viewpoint of the other nodes, they are communicating with the present node using the virtual queue pair and not the physical queue pair for the present node. By using the virtual queue pairs, the same physical queue pair may accommodate multiple connections with other nodes simultaneously. Moreover, by using a virtual queue pair rather than a physical queue pair, when a connection is torn down, the virtual queue pair is placed in a time-wait state rather than the physical queue pair. As a result, the physical queue pair may continue to function while the virtual queue pair is in the time-wait state.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention is directed to an improved data processingsystem. More specifically, the present invention is directed to anapparatus and method for virtualizing a queue pair space to minimizetime-wait impacts.

[0003] 2. Description of Related Art

[0004] In a System Area Network (SAN), the hardware provides a messagepassing mechanism that can be used for Input/Output devices (I/O) andinterprocess communications (IPC) between general computing nodes.Processes executing on devices access SAN message passing hardware byposting send/receive messages to send/receive work queues on a SANchannel adapter (CA). These processes also are referred to as“consumers.”

[0005] The send/receive work queues (WQ) are assigned to a consumer as aqueue pair (QP). The messages can be sent over five different transporttypes: Reliable Connected (RC), Reliable datagram (RD), UnreliableConnected (UC), Unreliable Datagram (UD), and Raw Datagram (RawD).Consumers retrieve the results of these messages from a completion queue(CQ) through SAN send and receive work completion (WC) queues. Thesource channel adapter takes care of segmenting outbound messages andsending them to the destination. The destination channel adapter takescare of reassembling inbound messages and placing them in the memoryspace designated by the destination's consumer.

[0006] Two channel adapter types are present in nodes of the SAN fabric,a host channel adapter (HCA) and a target channel adapter (TCA). Thehost channel adapter is used by general purpose computing nodes toaccess the SAN fabric. Consumers use SAN verbs to access host channeladapter functions. The software that interprets verbs and directlyaccesses the channel adapter is known as the channel interface (CI).

[0007] Target channel adapters (TCA) are used by nodes that are thesubject of messages sent from host channel adapters. The target channeladapters serve a similar function as that of the host channel adaptersin providing the target node an access point to the SAN fabric.

[0008] The SAN channel adapter architecture explicitly provides forsending and receiving messages directly from application programsrunning under an operating system. No intervention by the operatingsystem is required for an application program to post messages on sendqueues, post message receive buffers on receive queues, and detectcompletion of send or receive operations by polling of completion queuesor detecting the event of an entry stored on a completion queue, e.g.,via an interrupt.

[0009] When connections are established between nodes in a SAN fabric,physical queue pairs of channel adapters are typically used tofacilitate the connection. When these connections are torn down, thephysical queue pairs are placed in a time-wait state in order to makesure that all data packets in the SAN fabric at the time the connectionis torn down, have time to be routed to their destination. During thistime-wait state, the physical queue pairs cannot be used to establishnew connections with the same or other nodes. This results in aninefficiency in the SAN architecture with regard to the establishmentand tearing down of connections between nodes. Therefore, it would bebeneficial to have an apparatus and method for avoiding the time-waitstate delays experienced in typical SAN architectures.

SUMMARY OF THE INVENTION

[0010] An apparatus and method for virtualizing a queue pair space tominimize time-wait impacts. The apparatus and method allocate virtualqueue pairs from a virtual queue pair pool of a node to connectionsbetween the node and other nodes.

[0011] The connection is established between a physical queue pair ofthe node and a physical queue pair of another node. However, from theviewpoint of other nodes, they are communicating with the present nodeusing the virtual queue pair and not the physical queue pair for thepresent node.

[0012] By using the virtual queue pairs, the same physical queue pairmay be used for successive connections without the need to wait for thetimewait period to elapse. Moreover, by using a virtual queue pairrather than a physical queue pair, when a connection is torn down, thevirtual queue pair is placed in a time-wait state rather than thephysical queue pair. As a result, the physical queue pair may continueto function while the virtual queue pair is in the time-wait state

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The novel features believed characteristic of the invention areset forth in the appended claims. The invention itself, however, as wellas a preferred mode of use, further objectives and advantages thereof,will best be understood by reference to the following detaileddescription of an illustrative embodiment when read in conjunction withthe accompanying drawings, wherein:

[0014]FIG. 1 is a diagram of a distributed computer system isillustrated in accordance with a preferred embodiment of the presentinvention;

[0015]FIG. 2 is a functional block diagram of a host processor node inaccordance with a preferred embodiment of the present invention;

[0016]FIG. 3A is a diagram of a host channel adapter in accordance witha preferred embodiment of the present invention;

[0017]FIG. 3B is a diagram of a switch in accordance with a preferredembodiment of the present invention;

[0018]FIG. 3C is a diagram of a router in accordance with a preferredembodiment of the present invention;

[0019]FIG. 4 is a diagram illustrating processing of work requests inaccordance with a preferred embodiment of the present invention;

[0020]FIG. 5 is a diagram illustrating a portion of a distributedcomputer system in accordance with a preferred embodiment of the presentinvention in which a reliable connection service is used;

[0021]FIG. 6 is a diagram illustrating a portion of a distributedcomputer system in accordance with a preferred embodiment of the presentinvention in which reliable datagram service connections are used;

[0022]FIG. 7 is an illustration of a data packet in accordance with apreferred embodiment of the present invention;

[0023]FIG. 8 is a diagram illustrating a portion of a distributedcomputer system in accordance with a preferred embodiment of the presentinvention;

[0024]FIG. 9 is a diagram illustrating the network addressing used in adistributed networking system in accordance with the present invention;

[0025]FIG. 10 is a diagram illustrating a portion of a distributedcomputing system in accordance with a preferred embodiment of thepresent invention in which the structure of SAN fabric subnets isillustrated;

[0026]FIG. 11 is a diagram of a layered communication architecture usedin a preferred embodiment of the present invention;

[0027]FIG. 12 is an exemplary diagram illustrating a process forcreating a connection in a SAN architecture;

[0028]FIG. 13 is an exemplary diagram illustrating a process forreleasing or tearing down a connection in e a SAN architecture;

[0029]FIG. 14 is an exemplary diagram illustrating a connection betweentwo nodes in accordance with the present invention;

[0030]FIG. 15 is an exemplary diagram illustrating the re-use ofvirtualized queue pairs before a time-wait period expires;

[0031]FIG. 16 is a flowchart outlining an exemplary operation of thepresent invention; and

[0032]FIG. 17 is an exemplary diagram illustrating the application ofthe present invention to end-to-end contexts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0033] The present invention provides an apparatus and method forvirtualizing a queue pair space to minimize time-wait impacts. Thepresent invention may be implemented in hardware, software, or acombination of hardware and software. The present invention ispreferably implemented in a distributed computing system, such as asystem area network (SAN) having end nodes, switches, routers, and linksinterconnecting these components. Each end node uses send and receivequeue pairs to transmit and receives messages. The end nodes segment themessage into packets and transmit the packets over the links. Theswitches and routers interconnect the end nodes and route the packets tothe appropriate end node. The end nodes reassemble the packets into amessage at the destination.

[0034]FIG. 1 is a diagram of a distributed computer system in accordancewith a preferred embodiment of the present invention. The distributedcomputer system represented in FIG. 1 takes the form of a system areanetwork (SAN) 100 and is provided merely for illustrative purposes, andthe embodiments of the present invention described below can beimplemented on computer systems of numerous other types andconfigurations. For example, computer systems implementing the presentinvention can range from a small server with one processor and a fewinput/output (I/O) adapters to massively parallel supercomputer systemswith hundreds or thousands of processors and thousands of I/O adapters.Furthermore, the present invention can be implemented in aninfrastructure of remote computer systems connected by an Internet orintranet.

[0035] SAN 100 is a high-bandwidth, low-latency network interconnectingnodes within the distributed computer system. A node is any componentattached to one or more links of a network and forming the origin and/ordestination of messages within the network. In the depicted example, SAN100 includes nodes in the form of host processor node 102, hostprocessor node 104, redundant array independent disk (RAID) subsystemnode 106, and I/O chassis node 108. The nodes illustrated in FIG. 1 arefor illustrative purposes only, as SAN 100 can connect any number andany type of independent processor nodes, I/O adapter nodes, and I/Odevice nodes. Any one of the nodes can function as an endnode, which isherein defined to be a device that originates or finally consumesmessages or frames in SAN 100.

[0036] In one embodiment of the present invention, an error handlingmechanism in distributed computer systems is present in which the errorhandling mechanism allows for reliable connection or reliable datagramcommunication between end nodes in distributed computing system, such asSAN 100.

[0037] A message, as used herein, is an application-defined unit of dataexchange, which is a primitive unit of communication between cooperatingprocesses. A packet is one unit of data encapsulated by networkingprotocol headers and/or trailers. The headers generally provide controland routing information for directing the frame through SAN. The trailergenerally contains control and cyclic redundancy check (CRC) data forensuring packets are not delivered with corrupted contents.

[0038] SAN 100 contains the communications and management infrastructuresupporting both I/O and interprocessor communications (IPC) within adistributed computer system. The SAN 100 shown in FIG. 1 includes aswitched communications fabric 116, which allows many devices toconcurrently transfer data with high-bandwidth and low latency in asecure, remotely managed environment. Endnodes can communicate overmultiple ports and utilize multiple paths through the SAN fabric. Themultiple ports and paths through the SAN shown in FIG. 1 can be employedfor fault tolerance and increased bandwidth data transfers.

[0039] The SAN 100 in FIG. 1 includes switch 112, switch 114, switch146, and router 117. A switch is a device that connects multiple linkstogether and allows routing of packets from one link to another linkwithin a subnet using a small header Destination Local Identifier (DLID)field. A router is a device that connects multiple subnets together andis capable of routing frames from one link in a first subnet to anotherlink in a second subnet using a large header Destination Globally UniqueIdentifier (DGUID).

[0040] In one embodiment, a link is a full duplex channel between anytwo network fabric elements, such as endnodes, switches, or routers.Example suitable links include, but are not limited to, copper cables,optical cables, and printed circuit copper traces on backplanes andprinted circuit boards.

[0041] For reliable service types, endnodes, such as host processorendnodes and I/O adapter endnodes, generate request packets and returnacknowledgment packets. Switches and routers pass packets along, fromthe source to the destination. Except for the variant CRC trailer field,which is updated at each stage in the network, switches pass the packetsalong unmodified. Routers update the variant CRC trailer field andmodify other fields in the header as the packet is routed.

[0042] In SAN 100 as illustrated in FIG. 1, host processor node 102,host processor node 104, and I/O chassis 108 include at least onechannel adapter (CA) to interface to SAN 100. In one embodiment, eachchannel adapter is an endpoint that implements the channel adapterinterface in sufficient detail to source or sink packets transmitted onSAN fabric 100. Host processor node 102 contains channel adapters in theform of host channel adapter 118 and host channel adapter 120. Hostprocessor node 104 contains host channel adapter 122 and host channeladapter 124. Host processor node 102 also includes central processingunits 126-130 and a memory 132 interconnected by bus system 134. Hostprocessor node 104 similarly includes central processing units 136-140and a memory 142 interconnected by a bus system 144.

[0043] Host channel adapters 118 and 120 provide a connection to switch112 while host channel adapters 122 and 124 provide a connection toswitches 112 and 114.

[0044] In one embodiment, a host channel adapter is implemented inhardware. In this implementation, the host channel adapter hardwareoffloads much of central processing unit and I/O adapter communicationoverhead. This hardware implementation of the host channel adapter alsopermits multiple concurrent communications over a switched networkwithout the traditional overhead associated with communicatingprotocols. In one embodiment, the host channel adapters and SAN 100 inFIG. 1 provide the I/O and interprocessor communications (IPC) consumersof the distributed computer system with zero processor-copy datatransfers without involving the operating system kernel process, andemploys hardware to provide reliable, fault tolerant communications.

[0045] As indicated in FIG. 1, router 116 is coupled to wide areanetwork (WAN) and/or local area network (LAN) connections to other hostsor other routers. The I/O chassis 108 in FIG. 1 includes an I/O switch146 and multiple I/O modules 148-156. In these examples, the I/O modulestake the form of adapter cards. Example adapter cards illustrated inFIG. 1 include a SCSI adapter card for I/O module 148; an adapter cardto fiber channel hub and fiber channel-arbitrated loop (FC-AL) devicesfor I/O module 152; an ethernet adapter card for I/O module 150; agraphics adapter card for I/O module 154; and a video adapter card forI/O module 156. Any known type of adapter card can be implemented. I/Oadapters also include a switch in the I/O adapter backplane to couplethe adapter cards to the SAN fabric. These modules contain targetchannel adapters 158-166.

[0046] In this example, RAID subsystem node 106 in FIG. 1 includes aprocessor 168, a memory 170, a target channel adapter (TCA) 172, andmultiple redundant and/or striped storage disk unit 174. Target channeladapter 172 can be a fully functional host channel adapter.

[0047] SAN 100 handles data communications for I/O and interprocessorcommunications. SAN 100 supports high-bandwidth and scalability requiredfor I/O and also supports the extremely low latency and low CPU overheadrequired for interprocessor communications. User clients can bypass theoperating system kernel process and directly access networkcommunication hardware, such as host channel adapters, which enableefficient message passing protocols. SAN 100 is suited to currentcomputing models and is a building block for new forms of I/O andcomputer cluster communication. Further, SAN 100 in FIG. 1 allows I/Oadapter nodes to communicate among themselves or communicate with any orall of the processor nodes in distributed computer system. With an I/Oadapter attached to the SAN 100, the resulting I/O adapter node hassubstantially the same communication capability as any host processornode in SAN 100.

[0048] In one embodiment, the SAN 100 shown in FIG. 1 supports channelsemantics and memory semantics. Channel semantics is sometimes referredto as send/receive or push communication operations. Channel semanticsare the type of communications employed in a traditional I/O channelwhere a source device pushes data and a destination device determines afinal destination of the data. In channel semantics, the packettransmitted from a source process specifies a destination processes'communication port, but does not specify where in the destinationprocesses' memory space the packet will be written. Thus, in channelsemantics, the destination process pre-allocates where to place thetransmitted data.

[0049] In memory semantics, a source process directly reads or writesthe virtual address space of a remote node destination process. Theremote destination process need only communicate the location of abuffer for data, and does not need to be involved in the transfer of anydata. Thus, in memory semantics, a source process sends a data packetcontaining the destination buffer memory address of the destinationprocess. In memory semantics, the destination process previously grantspermission for the source process to access its memory.

[0050] Channel semantics and memory semantics are typically bothnecessary for I/O and interprocessor communications. A typical I/Ooperation employs a combination of channel and memory semantics. In anillustrative example I/O operation of the distributed computer systemshown in FIG. 1, a host processor node, such as host processor node 102,initiates an I/O operation by using channel semantics to send a diskwrite command to a disk I/O adapter, such as RAID subsystem targetchannel adapter (TCA) 172. The disk I/O adapter examines the command anduses memory semantics to read the data buffer directly from the memoryspace of the host processor node. After the data buffer is read, thedisk I/O adapter employs channel semantics to push an I/O completionmessage back to the host processor node.

[0051] In one exemplary embodiment, the distributed computer systemshown in FIG. 1 performs operations that employ virtual addresses andvirtual memory protection mechanisms to ensure correct and proper accessto all memory. Applications running in such a distributed computedsystem are not required to use physical addressing for any operations.

[0052] Turning next to FIG. 2, a functional block diagram of a hostprocessor node is depicted in accordance with a preferred embodiment ofthe present invention. Host processor node 200 is an example of a hostprocessor node, such as host processor node 102 in FIG. 1. In thisexample, host processor node 200 shown in FIG. 2 includes a set ofconsumers 202-208, which are processes executing on host processor node200. Host processor node 200 also includes channel adapter 210 andchannel adapter 212. Channel adapter 210 contains ports 214 and 216while channel adapter 212 contains ports 218 and 220. Each port connectsto a link. The ports can connect to one SAN subnet or multiple SANsubnets, such as SAN 100 in FIG. 1. In these examples, the channeladapters take the form of host channel adapters.

[0053] Consumers 202-208 transfer messages to the SAN via the verbsinterface 222 and message and data service 224. A verbs interface isessentially an abstract description of the functionality of a hostchannel adapter. An operating system may expose some or all of the verbfunctionality through its programming interface. Basically, thisinterface defines the behavior of the host. Additionally, host processornode 200 includes a message and data service 224, which is ahigher-level interface than the verb layer and is used to processmessages and data received through channel adapter 210 and channeladapter 212. Message and data service 224 provides an interface toconsumers 202-208 to process messages and other data.

[0054] With reference now to FIG. 3A, a diagram of a host channeladapter is depicted in accordance with a preferred embodiment of thepresent invention. Host channel adapter 300A shown in FIG. 3A includes aset of queue pairs (QPs) 302A-310A, which are used to transfer messagesto the host channel adapter ports 312A-316A. Buffering of data to hostchannel adapter ports 312A-316A is channeled through virtual lanes (VL)318A-334A where each VL has its own flow control. Subnet managerconfigures channel adapters with the local addresses for each physicalport, i.e., the port's LID. Subnet manager agent (SMA) 336A is theentity that communicates with the subnet manager for the purpose ofconfiguring the channel adapter. Memory translation and protection (MTP)338A is a mechanism that translates virtual addresses to physicaladdresses and validates access rights. Direct memory access (DMA) 340Aprovides for direct memory access operations using memory 340A withrespect to queue pairs 302A-310A.

[0055] A single channel adapter, such as the host channel adapter 300Ashown in FIG. 3A, can support thousands of queue pairs. By contrast, atarget channel adapter in an I/O adapter typically supports a muchsmaller number of queue pairs. Each queue pair consists of a send workqueue (SWQ) and a receive work queue. The send work queue is used tosend channel and memory semantic messages. The receive work queuereceives channel semantic messages. A consumer calls an operating-systemspecific programming interface, which is herein referred to as verbs, toplace work requests (WRs) onto a work queue.

[0056]FIG. 3B depicts a switch 300B in accordance with a preferredembodiment of the present invention. Switch 300B includes a packet relay302B in communication with a number of ports 304B through virtual lanessuch as virtual lane 306B. Generally, a switch such as switch 300B canroute packets from one port to any other port on the same switch.

[0057] Similarly, FIG. 3C depicts a router 300C according to a preferredembodiment of the present invention. Router 300C includes a packet relay302C in communication with a number of ports 304C through virtual lanessuch as virtual lane 306C. Like switch 300B, router 300C will generallybe able to route packets from one port to any other port on the samerouter.

[0058] Channel adapters, switches, and routers employ multiple virtuallanes within a single physical link. As illustrated in FIGS. 3A, 3B, and3C, physical ports connect endnodes, switches, and routers to a subnet.Packets injected into the SAN fabric follow one or more virtual lanesfrom the packet's source to the packet's destination. The virtual lanethat is selected is mapped from a service level associated with thepacket. At any one time, only one virtual lane makes progress on a givenphysical link. Virtual lanes provide a technique for applying link levelflow control to one virtual lane without affecting the other virtuallanes. When a packet on one virtual lane blocks due to contention,quality of service (QoS), or other considerations, a packet on adifferent virtual lane is allowed to make progress. Virtual lanes areemployed for numerous reasons, some of which are as follows: Virtuallanes provide QoS. In one example embodiment, certain virtual lanes arereserved for high priority or isochronous traffic to provide QoS.

[0059] Virtual lanes provide deadlock avoidance. Virtual lanes allowtopologies that contain loops to send packets across all physical linksand still be assured the loops won't cause back pressure dependenciesthat might result in deadlock.

[0060] Virtual lanes alleviate head-of-line blocking. When a switch hasno more credits available for packets that utilize a given virtual lane,packets utilizing a different virtual lane that has sufficient creditsare allowed to make forward progress.

[0061] With reference now to FIG. 4, a diagram illustrating processingof work requests is depicted in accordance with a preferred embodimentof the present invention. In FIG. 4, a receive work queue 400, send workqueue 402, and completion queue 404 are present for processing requestsfrom and for consumer 406. These requests from consumer 402 areeventually sent to hardware 408. In this example, consumer 406 generateswork requests 410 and 412 and receives work completion 414. As shown inFIG. 4, work requests placed onto a work queue are referred to as workqueue elements (WQEs).

[0062] Send work queue 402 contains work queue elements (WQEs) 422-428,describing data to be transmitted on the SAN fabric. Receive work queue400 contains work queue elements (WQEs) 416-420, describing where toplace incoming channel semantic data from the SAN fabric. A work queueelement is processed by hardware 408 in the host channel adapter.

[0063] The verbs also provide a mechanism for retrieving completed workfrom completion queue 404. As shown in FIG. 4, completion queue 404contains completion queue elements (CQEs) 430-436. Completion queueelements contain information about previously completed work queueelements. Completion queue 404 is used to create a single point ofcompletion notification for multiple queue pairs. A completion queueelement is a data structure on a completion queue. This elementdescribes a completed work queue element. The completion queue elementcontains sufficient information to determine the queue pair and specificwork queue element that completed. A completion queue context is a blockof information that contains pointers to, length, and other informationneeded to manage the individual completion queues.

[0064] Example work requests supported for the send work queue 402 shownin FIG. 4 are as follows. A send work request is a channel semanticoperation to push a set of local data segments to the data segmentsreferenced by a remote node's receive work queue element. For example,work queue element 428 contains references to data segment 4 438, datasegment 5 440, and data segment 6 442. Each of the send work request'sdata segments contains a virtually contiguous memory region. The virtualaddresses used to reference the local data segments are in the addresscontext of the process that created the local queue pair.

[0065] A remote direct memory access (RDMA) read work request provides amemory semantic operation to read a virtually contiguous memory space ona remote node. A memory space can either be a portion of a memory regionor portion of a memory window. A memory region references a previouslyregistered set of virtually contiguous memory addresses defined by avirtual address and length. A memory window references a set ofvirtually contiguous memory addresses that have been bound to apreviously registered region.

[0066] The RDMA Read work request reads a virtually contiguous memoryspace on a remote endnode and writes the data to a virtually contiguouslocal memory space. Similar to the send work request, virtual addressesused by the RDMA Read work queue element to reference the local datasegments are in the address context of the process that created thelocal queue pair. For example, work queue element 416 in receive workqueue 400 references data segment 1 444, data segment 2 446, and datasegment 448. The remote virtual addresses are in the address context ofthe process owning the remote queue pair targeted by the RDMA Read workqueue element.

[0067] A RDMA Write work queue element provides a memory semanticoperation to write a virtually contiguous memory space on a remote node.The RDMA Write work queue element contains a scatter list of localvirtually contiguous memory spaces and the virtual address of the remotememory space into which the local memory spaces are written.

[0068] A RDMA FetchOp work queue element provides a memory semanticoperation to perform an atomic operation on a remote word. The RDMAFetchOp work queue element is a combined RDMA Read, Modify, and RDMAWrite operation. The RDMA FetchOp work queue element can support severalread-modify-write operations, such as Compare and Swap if equal.

[0069] A bind (unbind) remote access key (R_Key) work queue elementprovides a command to the host channel adapter hardware to modify(destroy) a memory window by associating (disassociating) the memorywindow to a memory region. The R_Key is part of each RDMA access and isused to validate that the remote process has permitted access to thebuffer.

[0070] In one embodiment, receive work queue 400 shown in FIG. 4 onlysupports one type of work queue element, which is referred to as areceive work queue element. The receive work queue element provides achannel semantic operation describing a local memory space into whichincoming send messages are written. The receive work queue elementincludes a scatter list describing several virtually contiguous memoryspaces. An incoming send message is written to these memory spaces. Thevirtual addresses are in the address context of the process that createdthe local queue pair.

[0071] For interprocessor communications, a user-mode software processtransfers data through queue pairs directly from where the bufferresides in memory. In one embodiment, the transfer through the queuepairs bypasses the operating system and consumes few host instructioncycles. Queue pairs permit zero processor-copy data transfer with nooperating system kernel involvement. The zero processor-copy datatransfer provides for efficient support of high-bandwidth andlow-latency communication.

[0072] When a queue pair is created, the queue pair is set to provide aselected type of transport service. In one embodiment, a distributedcomputer system implementing the present invention supports four typesof transport services: reliable, unreliable, reliable datagram, andunreliable datagram connection service.

[0073] Reliable and Unreliable connected services associate a localqueue pair with one and only one remote queue pair. Connected servicesrequire a process to create a queue pair for each process that is tocommunicate with over the SAN fabric. Thus, if each of N host processornodes contain P processes, and all P processes on each node wish tocommunicate with all the processes on all the other nodes, each hostprocessor node requires P²×(N−1) queue pairs. Moreover, a process canconnect a queue pair to another queue pair on the same host channeladapter.

[0074] A portion of a distributed computer system employing a reliableconnection service to communicate between distributed processes isillustrated generally in FIG. 5. The distributed computer system 500 inFIG. 5 includes a host processor node 1, a host processor node 2, and ahost processor node 3. Host processor node 1 includes a process A 510.Host processor node 2 includes a process C 520 and a process D 530. Hostprocessor node 3 includes a process E 540.

[0075] Host processor node 1 includes queue pairs 4, 6 and 7, eachhaving a send work queue and receive work queue. Host processor node 2has a queue pair 9 and host processor node 3 has queue pairs 2 and 5.The reliable connection service of distributed computer system 500associates a local queue pair with one an only one remote queue pair.Thus, the queue pair 4 is used to communicate with queue pair 2; queuepair 7 is used to communicate with queue pair 5; and queue pair 6 isused to communicate with queue pair 9.

[0076] A WQE placed on one queue pair in a reliable connection servicecauses data to be written into the receive memory space referenced by aReceive WQE of the connected queue pair. RDMA operations operate on theaddress space of the connected queue pair.

[0077] In one embodiment of the present invention, the reliableconnection service is made reliable because hardware maintains sequencenumbers and acknowledges all packet transfers. A combination of hardwareand SAN driver software retries any failed communications. The processclient of the queue pair obtains reliable communications even in thepresence of bit errors, receive underruns, and network congestion. Ifalternative paths exist in the SAN fabric, reliable communications canbe maintained even in the presence of failures of fabric switches,links, or channel adapter ports.

[0078] In addition, acknowledgments may be employed to deliver datareliably across the SAN fabric. The acknowledgment may, or may not, be aprocess level acknowledgment, i.e. an acknowledgment that validates thata receiving process has consumed the data. Alternatively, theacknowledgment may be one that only indicates that the data has reachedits destination.

[0079] Reliable datagram service associates a local end-to-end context(EEC) with one and only one remote end-to-end context. The reliabledatagram service permits a client process of one queue pair tocommunicate with any other queue pair on any other remote node. At areceive work queue, the reliable datagram service permits incomingmessages from any send work queue on any other remote node.

[0080] The reliable datagram service greatly improves scalabilitybecause the reliable datagram service is connectionless. Therefore, anendnode with a fixed number of queue pairs can communicate with far moreprocesses and endnodes with a reliable datagram service than with areliable connection transport service. For example, if each of N hostprocessor nodes contain P processes, and all P processes on each nodewish to communicate with all the processes on all the other nodes, thereliable connection service requires P²×(N−1) queue pairs on each node.By comparison, the connectionless reliable datagram service onlyrequires P queue pairs+(N−1) EE contexts on each node for exactly thesame communications.

[0081] A portion of a distributed computer system employing a reliabledatagram service to communicate between distributed processes isillustrated in FIG. 6. The distributed computer system 600 in FIG. 6includes a host processor node 1, a host processor node 2, and a hostprocessor node 3. Host processor node 1 includes a process A 610 havinga queue pair 4. Host processor node 2 has a process C 620 having a queuepair 24 and a process D 630 having a queue pair 25. Host processor node3 has a process E 640 having a queue pair 14.

[0082] In the reliable datagram service implemented in the distributedcomputer system 600, the queue pairs are coupled in what is referred toas a connectionless transport service. For example, a reliable datagramservice couples queue pair 4 to queue pairs 24, 25 and 14. Specifically,a reliable datagram service allows queue pair 4's send work queue toreliably transfer messages to receive work queues in queue pairs 24, 25and 14. Similarly, the send queues of queue pairs 24, 25, and 14 canreliably transfer messages to the receive work queue in queue pair 4.

[0083] In one embodiment of the present invention, the reliable datagramservice employs sequence numbers and acknowledgments associated witheach message frame to ensure the same degree of reliability as thereliable connection service. End-to-end (EE) contexts maintainend-to-end specific state to keep track of sequence numbers,acknowledgments, and time-out values. The end-to-end state held in theEE contexts is shared by all the connectionless queue pairscommunication between a pair of endnodes. Each endnode requires at leastone EE context for every endnode it wishes to communicate with in thereliable datagram service (e.g., a given endnode requires at least N EEcontexts to be able to have reliable datagram service with N otherendnodes).

[0084] The unreliable datagram service is connectionless. The unreliabledatagram service is employed by management applications to discover andintegrate new switches, routers, and endnodes into a given distributedcomputer system. The unreliable datagram service does not provide thereliability guarantees of the reliable connection service and thereliable datagram service. The unreliable datagram service accordinglyoperates with less state information maintained at each endnode.

[0085] Turning next to FIG. 7, an illustration of a data packet isdepicted in accordance with a preferred embodiment of the presentinvention. A data packet is a unit of information that is routed throughthe SAN fabric. The data packet is an endnode-to-endnode construct, andis thus created and consumed by endnodes. For packets destined to achannel adapter (either host or target), the data packets are neithergenerated nor consumed by the switches and routers in the SAN fabric.Instead for data packets that are destined to a channel adapter,switches and routers simply move request packets or acknowledgmentpackets closer to the ultimate destination, modifying the variant linkheader fields in the process. Routers, also modify the packet's networkheader when the packet crosses a subnet boundary. In traversing asubnet, a single packet stays on a single service level.

[0086] Message data 700 contains data segment 1 702, data segment 2 704,and data segment 3 706, which are similar to the data segmentsillustrated in FIG. 4. In this example, these data segments form apacket 708, which is placed into packet payload 710 within data packet712. Additionally, data packet 712 contains CRC 714, which is used forerror checking. Additionally, routing header 716 and transport 718 arepresent in data packet 712. Routing header 716 is used to identifysource and destination ports for data packet 712. Transport header 718in this example specifies the destination queue pair for data packet712. Additionally, transport header 718 also provides information suchas the operation code, packet sequence number, and partition for datapacket 712.

[0087] The operating code identifies whether the packet is the first,last, intermediate, or only packet of a message. The operation code alsospecifies whether the operation is a send RDMA write, read, or atomic.The packet sequence number is initialized when communication isestablished and increments each time a queue pair creates a new packet.Ports of an endnode may be configured to be members of one or morepossibly overlapping sets called partitions.

[0088] In FIG. 8, a portion of a distributed computer system is depictedto illustrate an example request and acknowledgment transaction. Thedistributed computer system in FIG. 8 includes a host processor node 802and a host processor node 804. Host processor node 802 includes a hostchannel adapter 806. Host processor node 804 includes a host channeladapter 808. The distributed computer system in FIG. 8 includes a SANfabric 810, which includes a switch 812 and a switch 814. The SAN fabricincludes a link coupling host channel adapter 806 to switch 812; a linkcoupling switch 812 to switch 814; and a link coupling host channeladapter 808 to switch 814.

[0089] In the example transactions, host processor node 802 includes aclient process A. Host processor node 804 includes a client process B.Client process A interacts with host channel adapter hardware 806through queue pair 824. Client process B interacts with hardware channeladapter hardware 808 through queue pair 828. Queue pairs 824 and 828 aredata structures that include a send work queue and a receive work queue.Process A initiates a message request by posting work queue elements tothe send queue of queue pair 824. Such a work queue element isillustrated in FIG. 4. The message request of client process A isreferenced by a gather list contained in the send work queue element.Each data segment in the gather list points to a virtually contiguouslocal memory region, which contains a part of the message, such asindicated by data segments 1, 2, and 3, which respectively hold messageparts 1, 2, and 3, in FIG. 4.

[0090] Hardware in host channel adapter 806 reads the work queue elementand segments the message stored in virtual contiguous buffers into datapackets, such as the data packet illustrated in FIG. 7. Data packets arerouted through the SAN fabric, and for reliable transfer services, areacknowledged by the final destination endnode. If not successivelyacknowledged, the data packet is retransmitted by the source endnode.Data packets are generated by source endnodes and consumed bydestination endnodes.

[0091] In reference to FIG. 9, a diagram illustrating the networkaddressing used in a distributed networking system is depicted inaccordance with the present invention. A host name provides a logicalidentification for a host node, such as a host processor node or I/Oadapter node. The host name identifies the endpoint for messages suchthat messages are destined for processes residing on an end nodespecified by the host name. Thus, there is one host name per node, but anode can have multiple CAs. A single IEEE assigned 64-bit identifier(EUI-64) 902 is assigned to each component. A component can be a switch,router, or CA.

[0092] One or more globally unique ID (GUID) identifiers 904 areassigned per CA port 906. Multiple GUIDs (a.k.a. IP addresses) can beused for several reasons, some of which are illustrated by the followingexamples. In one embodiment, different IP addresses identify differentpartitions or services on an end node. In a different embodiment,different IP addresses are used to specify different Quality of Service(QoS) attributes. In yet another embodiment, different IP addressesidentify different paths through intra-subnet routes.

[0093] One GUID 908 is assigned to a switch 910.

[0094] A local ID (LID) refers to a short address ID used to identify aCA port within a single subnet. In one example embodiment, a subnet hasup to 2¹⁶ end nodes, switches, and routers, and the LID is accordingly16 bits. A source LID (SLID) and a destination LID (DLID) are the sourceand destination LIDs used in a local network header. A single CA port1006 has up to 2^(LMC) LIDs 912 assigned to it. The LMC represents theLID Mask Control field in the CA. A mask is a pattern of bits used toaccept or reject bit patterns in another set of data.

[0095] Multiple LIDs can be used for several reasons some of which areprovided by the following examples. In one embodiment, different LIDsidentify different partitions or services in an end node. In anotherembodiment, different LIDs are used to specify different QoS attributes.In yet a further embodiment, different LIDs specify different pathsthrough the subnet. A single switch port 914 has one LID 916 associatedwith it.

[0096] A one-to-one correspondence does not necessarily exist betweenLIDs and GUIDs, because a CA can have more or less LIDs than GUIDs foreach port. For CAs with redundant ports and redundant connectivity tomultiple SAN fabrics, the CAs can, but are not required to, use the sameLID and GUID on each of its ports.

[0097] A portion of a distributed computer system in accordance with apreferred embodiment of the present invention is illustrated in FIG. 10.Distributed computer system 1000 includes a subnet 1002 and a subnet1004. Subnet 1002 includes host processor nodes 1006, 1008, and 1010.Subnet 1004 includes host processor nodes 1012 and 1014. Subnet 1002includes switches 1016 and 1018. Subnet 1004 includes switches 1020 and1022.

[0098] Routers connect subnets. For example, subnet 1002 is connected tosubnet 1004 with routers 1024 and 1026. In one example embodiment, asubnet has up to 216 endnodes, switches, and routers.

[0099] A subnet is defined as a group of endnodes and cascaded switchesthat is managed as a single unit. Typically, a subnet occupies a singlegeographic or functional area. For example, a single computer system inone room could be defined as a subnet. In one embodiment, the switchesin a subnet can perform very fast wormhole or cut-through routing formessages.

[0100] A switch within a subnet examines the DLID that is unique withinthe subnet to permit the switch to quickly and efficiently routeincoming message packets. In one embodiment, the switch is a relativelysimple circuit, and is typically implemented as a single integratedcircuit. A subnet can have hundreds to thousands of endnodes formed bycascaded switches.

[0101] As illustrated in FIG. 10, for expansion to much larger systems,subnets are connected with routers, such as routers 1024 and 1026. Therouter interprets the IP destination ID (e.g., IPv6 destination ID) androutes the IP-like packet.

[0102] An example embodiment of a switch is illustrated generally inFIG. 3B. Each I/O path on a switch or router has a port. Generally, aswitch can route packets from one port to any other port on the sameswitch.

[0103] Within a subnet, such as subnet 1002 or subnet 1004, a path froma source port to a destination port is determined by the LID of thedestination host channel adapter port. Between subnets, a path isdetermined by the IP address (e.g., IPv6 address) of the destinationhost channel adapter port and by the LID address of the router portwhich will be used to reach the destination's subnet.

[0104] In one embodiment, the paths used by the request packet and therequest packet's corresponding positive acknowledgment (ACK) or negativeacknowledgment (NAK) frame are not required to be symmetric. In oneembodiment employing certain routing, switches select an output portbased on the DLID. In one embodiment, a switch uses one set of routingdecision criteria for all its input ports. In one example embodiment,the routing decision criteria are contained in one routing table. In analternative embodiment, a switch employs a separate set of criteria foreach input port.

[0105] A data transaction in the distributed computer system of thepresent invention is typically composed of several hardware and softwaresteps. A client process data transport service can be a user-mode or akernel-mode process. The client process accesses host channel adapterhardware through one or more queue pairs, such as the queue pairsillustrated in FIGS. 3A, 5, and 6. The client process calls anoperating-system specific programming interface, which is hereinreferred to as “verbs.” The software code implementing verbs posts awork queue element to the given queue pair work queue.

[0106] There are many possible methods of posting a work queue elementand there are many possible work queue element formats, which allow forvarious cost/performance design points, but which do not affectinteroperability. A user process, however, must communicate to verbs ina well-defined manner, and the format and protocols of data transmittedacross the SAN fabric must be sufficiently specified to allow devices tointeroperate in a heterogeneous vendor environment.

[0107] In one embodiment, channel adapter hardware detects work queueelement postings and accesses the work queue element. In thisembodiment, the channel adapter hardware translates and validates thework queue element's virtual addresses and accesses the data.

[0108] An outgoing message is split into one or more data packets. Inone embodiment, the channel adapter hardware adds a transport header anda network header to each packet. The transport header includes sequencenumbers and other transport information. The network header includesrouting information, such as the destination IP address and othernetwork routing information. The link header contains the DestinationLocal Identifier (DLID) or other local routing information. Theappropriate link header is always added to the packet. The appropriateglobal network header is added to a given packet if the destinationendnode resides on a remote subnet.

[0109] If a reliable transport service is employed, when a request datapacket reaches its destination endnode, acknowledgment data packets areused by the destination endnode to let the request data packet senderknow the request data packet was validated and accepted at thedestination. Acknowledgment data packets acknowledge one or more validand accepted request data packets. The requester can have multipleoutstanding request data packets before it receives any acknowledgments.In one embodiment, the number of multiple outstanding messages, i.e.Request data packets, is determined when a queue pair is created.

[0110] One embodiment of a layered architecture 1100 for implementingthe present invention is generally illustrated in diagram form in FIG.11. The layered architecture diagram of FIG. 11 shows the various layersof data communication paths, and organization of data and controlinformation passed between layers.

[0111] Host channel adapter endnode protocol layers (employed by endnode1111, for instance) include an upper level protocol 1102 defined byconsumer 1103, a transport layer 1104; a network layer 1106, a linklayer 1108, and a physical layer 1110. Switch layers (employed by switch1113, for instance) include link layer 1108 and physical layer 1110.Router layers (employed by router 1115, for instance) include networklayer 1106, link layer 1108, and physical layer 1110.

[0112] Layered architecture 1100 generally follows an outline of aclassical communication stack. With respect to the protocol layers ofend node 1111, for example, upper layer protocol 1102 employs verbs(1112) to create messages at transport layer 1104. Transport layer 1104passes messages (1114) to network layer 1106. Network layer 1106 routespackets between network subnets (1116). Link layer 1108 routes packetswithin a network subnet (1118). Physical layer 1110 sends bits or groupsof bits to the physical layers of other devices. Each of the layers isunaware of how the upper or lower layers perform their functionality.

[0113] Consumers 1103 and 1105 represent applications or processes thatemploy the other layers for communicating between endnodes. Transportlayer 1104 provides end-to-end message movement. In one embodiment, thetransport layer provides four types of transport services as describedabove which are reliable connection service; reliable datagram service;unreliable datagram service; and raw datagram service. Network layer1106 performs packet routing through a subnet or multiple subnets todestination endnodes. Link layer 1108 performs flow-controlled, errorchecked, and prioritized packet delivery across links.

[0114] Physical layer 1110 performs technology-dependent bittransmission. Bits or groups of bits are passed between physical layersvia links 1122, 1124, and 1126. Links can be implemented with printedcircuit copper traces, copper cable, optical cable, or with othersuitable links.

[0115] The present invention operates within the SAN environmentdescribed above with regard to FIGS. 1-11. The present inventionprovides a mechanism for virtualizing the queue pair space so that theimpact of Time-Wait is minimized.

[0116]FIG. 12 illustrates the process employed by a communicationmanager to establish a connection between queue pairs (QPs) orend-to-end contexts (EECs) on two different nodes. Typically, thecommunication manager resides in the host processor node initiating theconnection. However, the communication manager may reside in any othernode and the present invention is not limited to any particular locationof the communication manager.

[0117] As shown in FIG. 12, the communication management request (REQ)message is used to request the establishment of the connection. Thismessage is sent on a well-known QP (such as QP1) that is monitored bymanagement agents on all nodes, i.e. applications on the nodes used tomonitor queue pairs. If the management agent residing on the receivingnode wishes to accept the request for the connection establishment, themanagement agent indicates this by responding with a communicationmanagement reply (REP) message. The management agent decides whether toaccept a request or not based on a number of considerations such aswhether it supports the service type requested in the REQ packet,whether it supports the transport service type requested, and whether ithas resources, such as a QP, available for the connection.

[0118] When the requesting communication manager receives the REPmessage, the communication manager indicates its receipt and thatcommunication may begin, by sending a ready-to-use (RTU) message. TheREQ and REP messages contain information that identifies the type ofconnection requested and, in particular, the QP number (and EEC numberfor reliable datagram service) that the sending node wishes to use forthis connection.

[0119]FIG. 13 illustrates the process employed by a communicationmanager to release a connection between QPs or EECs on two differentnodes. The communication management disconnect request (DREQ) message isused to request the release of the connection. When the management agentresiding on the receiving node receives the DREQ, the management agentindicates that the connection may be released by responding with acommunication management disconnect reply (DREP) message. The DREQmessage contains an identifier that uniquely identifies the connectionto be released, and the QP number or EEC number of the remote node thatis associated with this connection.

[0120] When the responding node receives the DREQ, the responding nodeplaces the QP or EEC associated with this connection into a time-waitstate. During the time-wait state, the QP or EEC may not be used foranother connection, so essentially it remains idle. The time-wait stateis used to ensure that all data packets being transmitted along theoriginal connection are routed to their respective end nodes.

[0121] When the initiating node receives the DREP, the initiating nodeplaces its QP or EEC associated with this connection into the time-waitstate. The QP or EEC remains in the time-wait state for a sufficienttime to allow any packets or acknowledgments to traverse the SAN fabric,so that after the time-wait period has elapsed, there will be no morepackets received for this connection. If the QP was reused immediately,a packet may be received on the QP from the old connection (this isquite possible as there may be packets in flight that were sent beforethe DREQ was received). This packet may be misinterpreted as beingrelated to the new connection and may cause data integrity or securityexposures to the application.

[0122]FIG. 14 illustrates two nodes that have a connection establishedbetween two QPs. Node 1 1410 that is using the virtualization process ofthe present invention, has a large pool of virtualized QPs 1450 fromwhich one of the virtualized QPs 1452 may be allocated to the connectionbetween node 1 1410 and node 2 1420. The pool of virtualized QPs 1450 isinitially allocated at initialization time when the HCA and it physicalQPs are initialized. There is a bit associated with each virtualized QPthat indicates whether it is available or in the time-wait state. Thisbit and the QP number itself are the only resources associated with thevirtualized QP. This pool 1450 may be large and may have any number ofvirtual QPs. For example, the pool 1450 may use up to the full 24 bitnumber space for queue pairs, as it does not consume any real resourcesin the channel adapter (CA). The physical QP space is much smaller as itrequires hardware resources in the CA that are used for the transmissionand reception of packets.

[0123] When a virtualized QP, such as virtual QP 1452, is allocated to aconnection, that QP number is associated with the physical QP 1460 thatis used for the connection. The particular QP allocated to a connectionis selected using a selection scheme. The selection scheme may be anyknown selection scheme, such as simply allocating the next QP in thestack that is not being used and is not in a time-wait state, using arandom selection scheme, or the like. The communication managerrequesting the connection typically performs the allocation of the QP.

[0124] In the depicted example, Node 2 1420 is not using thevirtualization process of the present invention and thus, onlyassociates a physical QP number with the connection. While FIG. 14 showsonly Node 1 1410 using the virtualized QPs of the present invention, theinvention is not limited to such an exemplary embodiment. Rather, bothNodes 1 and 2 may make use of the present invention. In addition, theremay be any number of nodes upon which the present invention may beimplemented and the present invention is not limited to only connectionsbetween two nodes.

[0125] As part of the virtualization process, Node 1 1410 allocates QP21452 from the larger pool of virtualized QPs 1450 and associates thevirtual queue pair QP2 1452 with the physical queue pair QP 1460. Thedifference between the virtual queue pair QP2 1452 and the physicalqueue pair QP 1460 is that the physical QP is where the WQEs are storedand the virtualized QP only consumes a QP number and a bit to indicatewhether the virtual QP is available.

[0126] In all communication management messages associated with thisconnection the communication manager, which may be in either one of node1 or node 2, identifies Node 1's QP as virtual queue pair QP 2 1452, notphysical queue pair QP 1460. As depicted in FIG. 14, Node 1 1410 hasvirtual queue pair QP 2 1452 connected to physical queue pair QP 4 1470on Node 2 1410. From Node 2's perspective, it has physical queue pairQP4 1470 connected to virtual queue pair QP2 1452 on Node 1, and knowsnothing about the existence of physical queue pair QP 1460.

[0127] When the connection between virtual queue pair QP2 1452 andphysical queue pair QP4 1470 is no longer needed, the communicationmanager requests that the connection be disconnected using the DREQ andDREP protocol described earlier. The virtual queue pair QP2 1452 andphysical queue pair QP4 1470 are both placed in the time-wait state, andcannot be used again until the time-wait period has expired.

[0128] Now, suppose, as illustrated in FIG. 15, Process A on Node 1 1510needs to establish a connection with Process D on Node 2 1520. Node 21520 cannot re-use the physical queue pair QP4 1570 for this connectionuntil the time-wait period has expired. Therefore, Node 2 1520 must useanother physical queue pair, if there is one available.

[0129] As shown in FIG. 15, the physical queue pair QP5 1580 isallocated to the new connection. Similarly, Node 1 1510 cannot re-usevirtual queue pair QP2 1552 until the time-wait period has expired.However, QP2 1552 is a virtualized QP and is not consuming CA hardwareresources. Thus, another virtual queue pair QP from the virtualized pool1550 may be assigned to the new connection, e.g., virtual queue pair QP31554.

[0130] The physical queue pair QP 1560 may be reused for this newconnection because it has not been placed in a time-wait state. Thephysical queue pair QP 1560 is then associated with the virtual queuepair QP 3 1554 for this new connection. Thus, a new connection isestablished that connects virtual queue pair QP3 1554 on Node l withphysical queue pair QP 5 1580 on Node 2 1520. In both the new and theold connection the physical queue pair QP 1560 is used by Node 1 1510.Therefore, this optimizes the use of the hardware resources on the CA ofNode 1 1510.

[0131]FIG. 16 is a flowchart outlining an exemplary operation of thepresent invention. As shown in FIG. 16, the operation starts withreceiving a request to establish a new connection (step 1610). If thisrequest is from another node that is attempting to initiate aconnection, the request may be a REQ message.

[0132] A next virtual queue pair from the virtual queue pair pool isselected for the new connection (step 1620). A determination is made asto whether this virtual queue pair is in a time-wait state or is alreadyallocated to a connection (step 1630). If so, the operation returns tostep 1620 and the next virtual queue pair in the pool is allocated.

[0133] If the virtual queue pair is not in a time-wait state and is notalready allocated to a connection, the virtual queue pair is allocatedto the new connection (step 1640). A message is then sent to the othernode with which a communication connection is to be established (step1650). If the present node is the initiator, this message may be a REQmessage. If the present node is a receiver of a REQ message from aninitiating node, the message may be a REP message.

[0134] Thereafter, assuming that if the present node is the initiator aRTU message is received from the other node, communication between thetwo nodes may begin (step 1660). The operation then ends.

[0135] The preceding description illustrates how virtualized QPs can beused to optimize the use of hardware resources, when the transport typeis reliable connected or unreliable connected, a similar technique canbe used to virtualize end-to-end contexts and thus, save hardwareresources associated with an end-to-end context when using the ReliableDatagram transport type.

[0136]FIG. 17 illustrates the manner by which the present invention maybe applied to end-to-end contexts (EECs). As shown in FIG. 17, similarto the virtual queue pairs in the embodiments described above, a pool ofvirtual EECs is provided which may be allocated to connections betweennode 1 and node 2. These virtual EECs receive communications via thephysical QP of the node and the physical EECs, as shown. In the same waythat the virtual QPs are placed in a time-wait state when a connectionis torn down between node 1 and node 2, the virtual EECs are placed in atime-wait state when the connection between nodes 1 and 2 is torn down.This enables the physical EECs to be immediately reallocated to anotherconnection using a new virtual EEC, e.g., EEC2 in FIG. 17.

[0137] Thus, the present invention provides a virtualized queue pairpool that may be used in managing connections between physical queuepairs. By use of the virtualized queue pairs of the present invention,the problems associated with processes waiting for a time-wait period toexpire are avoided. That is, without this invention, new connectionrequests may need to be rejected until one or more time-wait periodshave elapsed to make the hardware resources available. In large fabricsthe time-wait period may be quite long. However, with the presentinvention, the hardware resources are made available immediately byvirtue of the virtualized queue pairs being placed in the time-waitstate.

[0138] It is important to note that while the present invention has beendescribed in the context of a fully functioning data processing system,those of ordinary skill in the art will appreciate that the processes ofthe present invention are capable of being distributed in the form of acomputer readable medium of instructions and a variety of forms and thatthe present invention applies equally regardless of the particular typeof signal bearing media actually used to carry out the distribution.Examples of computer readable media include recordable-type media suchas a floppy disk, a hard disk drive, a RAM, and CD-ROMs andtransmission-type media such as digital and analog communications links.

[0139] The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art. The embodiment was chosen and described in order to bestexplain the principles of the invention, the practical application, andto enable others of ordinary skill in the art to understand theinvention for various embodiments with various modifications as aresuited to the particular use contemplated.

What is claimed is:
 1. A method of establishing a connection between afirst node and a second node in a system area network, comprising:allocating a virtual connection unit pair to the connection, the virtualconnection unit pair being associated with the first node; establishingthe connection between the virtual connection unit pair of the firstnode and a connection unit pair of the second node; and transmitting oneor more messages between the first node and the second node over theconnection using the virtual connection unit pair.
 2. The method ofclaim 1, wherein the connection unit pair is a queue pair.
 3. The methodof claim 1, wherein the connection unit pair is an end-to-end context.4. The method of claim 1, wherein the virtual connection unit pair hasonly a virtual connection unit pair identifier and an availability bit.5. The method of claim 1, wherein allocating a virtual connection unitpair to the connection includes: selecting the virtual connection unitpair from a virtual connection unit pair pool; and associating a virtualconnection unit pair identifier of the virtual connection unit pair witha physical connection unit pair of the first node.
 6. The method ofclaim 1, further comprising: tearing down the connection between thefirst node and the second node, wherein tearing down the connectionincludes placing the virtual connection unit pair in a time-wait state.7. The method of claim 6, wherein a physical connection unit pairassociated with the first node is not placed in a time-wait state. 8.The method of claim 6, wherein a physical connection unit pairassociated with the first node is used to establish another connectionwhile the virtual connection unit pair is in the time-wait state.
 9. Themethod of claim 6, wherein placing the virtual connection unit pair in atime-wait state includes setting an availability bit associated with thevirtual connection unit pair.
 10. The method of claim 5, wherein thevirtual connection unit pair is selected from virtual connection unitpairs in the virtual connection unit pair pool that are not in atime-wait state.
 11. A computer program product in a computer readablemedium for establishing a connection between a first node and a secondnode in a system area network, comprising: first instructions forallocating a virtual connection unit pair to the connection, the virtualconnection unit pair being associated with the first node; secondinstructions for establishing the connection between the virtualconnection unit pair of the first node and a connection unit pair of thesecond node; and third instructions for transmitting one or moremessages between the first node and the second node over the connectionusing the virtual connection unit pair.
 12. The computer program productof claim 11, wherein the connection unit pair is a queue pair.
 13. Thecomputer program product of claim 11, wherein the connection unit pairis an end-to-end context.
 14. The computer program product of claim 11,wherein the virtual connection unit pair has only a virtual connectionunit pair identifier and an availability bit.
 15. The method of claim11, wherein the first instructions for allocating a virtual connectionunit pair to the connection includes: instructions for selecting thevirtual connection unit pair from a virtual connection unit pair pool;and instructions for associating a virtual connection unit pairidentifier of the virtual connection unit pair with a physicalconnection unit pair of the first node.
 16. The computer program productof claim 11, further comprising: fourth instructions for tearing downthe connection between the first node and the second node, wherein thefourth instructions for tearing down the connection include instructionsfor placing the virtual connection unit pair in a time-wait state. 17.The computer program product of claim 16, wherein a physical connectionunit pair associated with the first node is not placed in a time-waitstate.
 18. The computer program product of claim 16, wherein a physicalconnection unit pair associated with the first node is used to establishanother connection while the virtual connection unit pair is in thetime-wait state.
 19. The computer program product of claim 16, whereinthe instructions for placing the virtual connection unit pair in atime-wait state include instructions for setting an availability bitassociated with the virtual connection unit pair.
 20. The computerprogram product of claim 15, wherein the virtual connection unit pair isselected from virtual connection unit pairs in the virtual connectionunit pair pool that are not in a time-wait state.
 21. An apparatus forestablishing a connection between a first node and a second node in asystem area network, comprising: means for allocating a virtualconnection unit pair to the connection, the virtual connection unit pairbeing associated with the first node; means for establishing theconnection between the virtual connection unit pair of the first nodeand a connection unit pair of the second node; and means fortransmitting one or more messages between the first node and the secondnode over the connection using the virtual connection unit pair.
 22. Theapparatus of claim 21, wherein the connection unit pair is a queue pair.23. The apparatus of claim 21, wherein the connection unit pair is anend-to-end context.
 24. The apparatus of claim 21, wherein the virtualconnection unit pair has only a virtual connection unit pair identifierand an availability bit.
 25. The apparatus of claim 21, wherein themeans for allocating a virtual connection unit pair to the connectionincludes: means for selecting the virtual connection unit pair from avirtual connection unit pair pool; and means for associating a virtualconnection unit pair identifier of the virtual connection unit pair witha physical connection unit pair of the first node.
 26. The apparatus ofclaim 21, further comprising: means for tearing down the connectionbetween the first node and the second node, wherein the means fortearing down the connection includes means for placing the virtualconnection unit pair in a time-wait state.
 27. The apparatus of claim26, wherein a physical connection unit pair associated with the firstnode is not placed in a time-wait state.
 28. The apparatus of claim 26,wherein a physical connection unit pair associated with the first nodeis used to establish another connection while the virtual connectionunit pair is in the time-wait state.
 29. The apparatus of claim 26,wherein the means for placing the virtual connection unit pair in atime-wait state includes means for setting an availability bitassociated with the virtual connection unit pair.
 30. The apparatus ofclaim 25, wherein the virtual connection unit pair is selected fromvirtual connection unit pairs in the virtual connection unit pair poolthat are not in a time-wait state.